JPH02211940A - Mold for continuous casting - Google Patents

Abstract

PURPOSE:To suppress the development of surface defect at edge parts in a cast slab by arranging rapid cool preventing member having smooth curving face at casting wall of the range, in which at least initial solidified shell is formed, in corner part of a mold body having rectangular shape in cross section of the casting range. CONSTITUTION:By opening a tundish nozzle, molten steel is poured into the mold 10. By being brought into contact with the casting wall members 12, 14, the solidified shell is formed. The molten steel 5 is forcedly cooled with the casting wall members 12, 14 in long sides and short sides, but cooling effect of the members 12, 14 is relieved with the rapid cool preventing member 16 at the corner parts in the mold. In this way, excess cooling of the molten steel at the corner parts is eliminated, and the initial solidified shell 6 is grown at good balance even in the corner parts, and even in the case bulging develops, overlap of the thin solidified shells does not occur. As the rapid cool preventing member, heat resistant ceramic or metal may be used, but particularly copper or copper alloy is desirable. By this method, maintenance work, such as surface scarfing in the following stage, is scarcely necessary and also improvement of yield of a cast slab can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting mold, and particularly relates to an improvement of a continuous casting mold for continuously casting slabs for direct rolling.

[Prior Art] Recently, so-called hot direct rolling has been developed, in which a continuous casting machine and a rolling mill are directly connected, and the continuously cast slab is conveyed to the rolling mill while it is still in a high temperature state, and then immediately rolled in the hot state. (
(hereinafter referred to as HDR) has been developed. According to HDH, since the cast slab immediately after continuous casting is rolled without passing through a heating furnace, energy costs are significantly reduced and the demand for energy saving can be met.

In conventional continuous casting molds, for example, an assembled mold for slab casting, the casting area formed by the long side and short side is rectangular in cross section, and some of the corners thereof are substantially at right angles. There is.

[Problems to be Solved by the Invention] However, HDR products manufactured using conventional continuous casting molds tend to have many surface cracks at their edges, and require surface care such as scarfing in post-processes. The problem is that the work requires a lot of effort.

It is believed that such edge surface cracking of the HDR-subjected product occurs when the solidified shell within the mold does not grow sufficiently in the initial stage of solidification.

As shown in FIG. 3, in a part of the corner of the conventional assembled mold 2, the molten steel 5 is cooled two-dimensionally from both the long side 3 and the short side 4, and the thickness of the initial solidified shell 6 is smaller than that of the side. It gets thicker in some corners. For this reason, a thin region 7 where the solidified shell thickness is thinner occurs near a part of the corner, and when the side portion bulges, it is restrained by the solidified shell at the corner, and the solidified shells in the thin region 7 deform and overlap each other. This becomes a surface defect on the edge of the slab. Furthermore, due to the overlapping of the solidified shells, the powder is engulfed and dispersed.

Normally, in HDH, since the amount of peeling off of the slab surface scale due to rolling is small, it is difficult to completely remove surface defects at the edges of the slab, and the amount of cleaning work such as surface solvents increases in the subsequent process. There was a problem that the slab yield decreased.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a continuous casting mold that hardly causes surface defects on the edge of a slab, especially a continuous casting mold that does not substantially cause surface defects on the edge of a slab during direct rolling.

[Means for Solving the Problems] The continuous casting mold according to the present invention has a mold that has a sliding part in the corner part of the mold body whose casting area has a rectangular cross section and at least in the area where the initial solidified shell is formed. It is characterized by providing a rapid cooling prevention member having a kana curved surface.

[Function] In the continuous casting mold according to the present invention, since the quenching prevention member is provided at the corner of the mold, the development of an initial solidified shell at the corner is suppressed, and the solidification between the sides and the corner is prevented. Balanced shell thickness. Therefore, the constraint by the corner solidified shell is relaxed in the initial stage of casting, and even if bulging occurs, the initially solidified shell near the corner will not be substantially deformed, and surface defects due to the overlap of thin solidified shells will be avoided. It will no longer occur.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

A mold is installed in the upper part of the vertical bending continuous casting machine, and molten steel in the tundish is continuously injected into the mold through a submerged nozzle. A large number of guide rolls and spray nozzles are arranged below the mold so that the solidified shell slab pulled out from the mold is forcedly cooled while being guided.

Further, a large number of bending rolls are arranged below, and the slab is bent at a predetermined curvature of about 90'', so that the direction of drawing the slab is changed from vertical to horizontal. Pinch rolls, straightening rolls, etc. are installed on the upstream side, and an insulation zone of a predetermined length is installed on the downstream side.Furthermore, a rolling mill is installed downstream of the insulation zone, which completely solidifies the The slab is hot-rolled, that is, while the continuously cast slab is still at a high temperature, it is directly sent to a rolling mill and immediately rolled.

Next, the mold will be explained with reference to FIG.

The mold 10 is an assembly mold for a slab formed by combining a pair of long-side mold members 12 and a pair of short-side mold members 14.

Mold members 12,14 are each of water-cooled construction.

A rapid cooling prevention member 16 is provided at each inner corner of the mold 10. These quenching prevention members 16 are provided at the level where the initially solidified shell is formed, that is, in the upper region of the mold 10.

As shown in FIG. 2, a concave curved surface 17 is formed on the quenching prevention member 16, and the curved surface 17 is arranged so as to face the diagonal line of the mold. In this case, the quenching prevention member has a prismatic shape with a side of about 10 to 15-1, and the radius of curvature of the curved surface 17 is about 10-1. Note that the rapid cooling prevention member 16 is preferably made of either heat-resistant ceramic or metal, but is preferably made of copper or a copper alloy.

Next, a case will be described in which continuous casting of molten steel is performed using the above mold.

The tundish nozzle is opened and molten steel is injected into the mold 10. After a predetermined period of time has elapsed from the start of casting, the dummy bar is pulled out at a predetermined speed, and spray water is injected onto the unsolidified slab for forced cooling. When the molten steel is injected into the mold, it contacts the mold members 12.14 and forms a solidified shell. At this time, the molten steel 5 is forcibly cooled by the mold member 12.14 on the long and short sides, but the cooling effect of the member 12.14 is alleviated by the rapid cooling prevention member 16 in some mold corners. Therefore, excessive cooling of the molten steel in a part of the corner is eliminated, and as shown in Fig. 1, the initial solidified shell 6 grows in a well-balanced manner even in a part of the corner, and even if bulging etc. occurs, the thin solidified shells overlap ( (falling of the solidified shell toward the molten metal)
does not occur. Furthermore, the smooth curved surface 17 of the rapid cooling prevention member 16
Therefore, there is no mold powder entrainment, and a sound slab without surface defects at the edges can be obtained.

The thus continuously cast slab was directly sent to a rolling mill and directly rolled at a temperature of about 900° C. As a result, there were virtually no surface defects at the edges of the slab. For this reason, the incidence of rework on the slab surface was 3% in the past, but this is no longer necessary.

[Effects of the Invention] According to the present invention, by providing a quenching prevention member at the corner of the mold, it is possible to effectively suppress the occurrence of surface defects at the edge of the slab. The amount of rework can be significantly reduced. In particular, H
It is effective when the amount of scale peeled off from the surface of the slab during rolling is small, such as in DR, and it almost eliminates the need for cleaning the surface with a surface solvent in the subsequent process, and it is possible to improve the yield of the slab.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a continuous casting mold according to an embodiment of the present invention, FIG. 2 is a perspective view schematically showing a quenching prevention member at a corner of the mold, and FIG. 3 is a corner of a conventional mold. FIG. 3 is a cross-sectional area formula diagram for explaining the state of development of an initial solidified shell in a part. 10... Mold, 12.14... Casting wall member, 16...
・Rapid cooling prevention member, 17...Curved surface applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A corner of a mold body whose casting area has a rectangular cross section, and
A mold for continuous casting, characterized in that a quenching prevention member having a smooth curved surface is provided on the casting wall at least in a region where an initially solidified shell is formed.